The present invention relates to supplying printing inks to printing machines in general, and more particularly to a method of and an arrangement for normalized indication of printing ink supply to such machines.
There are already known various constructions of printing machines, among them rotary printing machines, such as offset printing machines, which are capable of printing in several colors. The present invention is directed especially but not exclusively to printing machines of the last-mentioned type, particularly such using a printing ink lifting element principle or a printing ink film transfer principle, both of which principles will be discussed in some detail below, for transferring the respective printing ink at a respective printing station from a ductor roller, which is partially immersed in a supply of the respective printing ink that is contained in a ductor box, to an associated first printing ink transfer roller.
The task of a printing ink supplying system in a printing machine is to withdraw the printing ink from a supply container (ductor box) and to feed the withdrawn printing ink to a printing ink spreading system at a rate which is metered in dependence on the requirements of the printing block.
The first of the principles mentioned above, which involves the use of a lifting element, especially a lifting roller, for discontinuous printing ink transfer from the ductor into the printing ink spreading system is being used, because of the high accuracy of the printing ink transfer, even in modern printing machines which operate at high speeds, especially in offset printing machines.
As is well known in this context, the lifting roller conducts a swinging motion so that it alternatively contacts the ductor roller and the first printing ink transfer roller of the printing ink spreading system. As a result of this swinging motion and the resulting temporary contact of the lifting roller with the ductor roller at one of the reversal points of the swinging motion of the lifting roller, a narrow strip of printing ink, which extends over the entire printing width of the printing machine and has a predetermined thickness and a given length in the circumferential direction of the lifting roller, is transferred from the ductor roller to the lifting roller; on the other hand, the amount of printing ink contained in this narrow printing ink strip is subsequently transferred from the lifting roller to the first printing ink transfer roller of the ink spreading system as the lifting roller contacts the first printing ink transfer roller at the other reversal point of the lifting roller swinging motion path.
When operating in accordance with the second-mentioned one of the above principles which involves the use of a printing ink transfer roller cooperating with the ductor roller, the printing ink is being continuously supplied to the printing ink spreading system. In this case, the printing ink transfer roller, which rotates at the same circumferential speed as the printing plate cylinder, continuously picks up a partial printing ink layer from the printing ink layer presented by the ductor roller, and transfers this partial printing ink layer to a following elastic roller of the printing ink spreading system. A gap is provided between the transfer roller and the ductor roller.
As will be shown later, the printing ink supply to the printing ink spreading system is dependent, in the final analysis, on the ratio of the rotational speed of the ductor roller driving motor to the rotational speed of the main driving motor of the printing machine. The rotational speed of the ductor roller driving motor is the parameter which is adjusted by the operator of the printing machine in order to adjust the supply of the printing ink per printing operation to the printing ink spreading system of the printing machine or of the printing station.
When the rotational speed of the main driving motor of the printing machine is changed, a control circuit incorporated in the printing machine control circuitry provides for a commensurate, that is, for relatively the same, change in the rotational speed of the ductor roller. In this manner, the amount of the printing ink transferred from the ductor roller to the printing ink spreading system is not influenced by such a change in the rotational speed of the main machine driving motor. Such ductor drives which are adjustable as far as their rotational speed is concerned and which are also regulated with respect to their rotational speed are generally known.
It is also known to construct the control system of the printing machine as to enable the printing machine operator to adjust the rotational speeds of the motors which drive the multitude of ductor rollers employed in the multicolor printing machine with the aid of centrally arranged indicating elements. However, in the known arrangements of this type, it is not the actual rotational speed (which, because of its coupling with the variable main machine drive, is not suited for use as an adjustment parameter) but rather the potentiometer angular displacement angle, the desired rotational speed, or another adjustment parameter which is adjusted instead, as disclosed, for instance, in the German Democratic Republic Patent DD-PS WP No. 125 618.
Regulation deviations of the control device which causes the rotational speed of the ductor roller to follow or be commensurate with the rotational speed of the main motor of the printing machine, as well as disturbing influences which are dependent on the speed or on the duration of operation of the printing machine, all of which cause the ductor roller printing ink layer thickness to vary, make it necessary for the printing machine operator to perform adjustment operations of the ductor roller rotational speeds both while the rotational speed of the main motor of the printing machine is being varied within the operational speed range of the main motor, and during the continuing operation of the printing machine even though the setting of the operating speed of the main motor is unchanged during such continuing operation, in such a manner as to maintain the supply of the printing ink per printing operation constant. Such an adjustment is currently being performed on the basis of the experience or intuition of the operating personnel, or only in reaction or response to color quality or color saturation in the printed product or the amount of misprints.